2,390 research outputs found
The axial anomaly in lattice QED. A universal point of view
We give a perturbative proof that U(1) lattice gauge theories generate the
axial anomaly in the continuum limit under very general conditions on the
lattice Dirac operator. These conditions are locality, gauge covariance and the
absense of species doubling. They hold for Wilson fermions as well as for
realizations of the Dirac operator that satisfy the Ginsparg-Wilson relation.
The proof is based on the lattice power counting theorem.Comment: 7 pages, Latex2e, some misprints removed, reference inserte
Lattice QED and Universality of the Axial Anomaly
We give a perturbative proof that U(1) lattice gauge theories generate the
axial anomaly in the continuum limit under very general conditions on the
lattice Dirac operator. These conditions are locality, gauge covariance and the
absense of species doubling. They hold for Wilson fermions as well as for
realizations of the Dirac operator that satisfy the Ginsparg-Wilson relation.
The proof is based on the lattice power counting theorem. The results
generalize to non-abelian gauge theories.Comment: LATTICE99(theoretical developments) 3 page
Renormalization of lattice gauge theories with massless Ginsparg Wilson fermions
Using functional techniques, we prove, to all orders of perturbation theory,
that lattice vector gauge theories with Ginsparg Wilson fermions are
renormalizable. For two or more massless fermions, they satisfy a flavour
mixing axial vector Ward identity. It involves a lattice specific part that is
quadratic in the vertex functional and classically irrelevant. We show that it
stays irrelevant under renormalization. This means that in the continuum limit
the (standard) chiral symmetry becomes restored. In particular, the flavour
mixing current does not require renormalization.Comment: 13 pages, Latex2
Cyclostationary shot noise in mesoscopic measurements
We discuss theoretically a setup where a time-dependent current consisting of
a DC bias and two sinusoidal harmonics is driven through a sample. If the
sample exhibits current-dependent shot noise, the down-converted noise power
spectrum varies depending on the local-oscillator phase of the mixer. The
theory of this phase-dependent noise is applied to discuss the measurement of
the radio-frequency single-electron transistor. We also show that this effect
can be used to measure the shot noise accurately even in nonlinear
high-impedance samples.Comment: 3 pages, 2 figure
Off-diagonal Gluon Mass Generation and Infrared Abelian Dominance in Maximally Abelian Gauge in SU(3) Lattice QCD
In SU(3) lattice QCD formalism, we propose a method to extract gauge fields
from link-variables analytically. With this method, we perform the first study
on effective mass generation of off-diagonal gluons and infrared Abelian
dominance in the maximally Abelian (MA) gauge in the SU(3) case. Using SU(3)
lattice QCD, we investigate the propagator and the effective mass of the gluon
fields in the MA gauge with U(1)_3 \timesU(1)_8 Landau gauge fixing. The
Monte Carlo simulation is performed on at =5.7, 5.8 and 6.0 at
the quenched level. The off-diagonal gluons behave as massive vector bosons
with the approximate effective mass in the region of fm, and the propagation is
limited within a short range, while the propagation of diagonal gluons remains
even in a large range. In this way, infrared Abelian dominance is shown in
terms of short-range propagation of off-diagonal gluons. Furthermore, we
investigate the functional form of the off-diagonal gluon propagator. The
functional form is well described by the four-dimensional Euclidean Yukawa-type
function with
for fm. This also indicates that the spectral function of
off-diagonal gluons has the negative-value region
Scalar-Quark Systems and Chimera Hadrons in SU(3)_c Lattice QCD
Light scalar-quarks \phi (colored scalar particles or idealized diquarks) and
their color-singlet hadronic states are studied with quenched SU(3)_c lattice
QCD in terms of mass generation in strong interaction without chiral symmetry
breaking. We investigate ``scalar-quark mesons'' \phi^\dagger \phi and
``scalar-quark baryons'' \phi\phi\phi which are the bound states of
scalar-quarks \phi. We also investigate the bound states of scalar-quarks \phi
and quarks \psi, i.e., \phi^\dagger \psi, \psi\psi\phi and \phi\phi\psi, which
we name ``chimera hadrons''. All the new-type hadrons including \phi are found
to have a large mass even for zero bare scalar-quark mass m_\phi=0 at
a^{-1}\simeq 1GeV. We find that the constituent scalar-quark and quark picture
is satisfied for all the new-type hadrons. Namely, the mass of the new-type
hadron composed of m \phi's and n \psi's, M_{{m}\phi+{n}\psi}, satisfies
M_{{m}\phi+{n}\psi}\simeq {m} M_\phi +{n} M_\psi, where M_\phi and M_\psi are
the constituent scalar-quark and quark mass, respectively. M_\phi at m_\phi=0
estimated from these new-type hadrons is 1.5-1.6GeV, which is larger than that
of light quarks, M_\psi\simeq 400{\rm MeV}. Therefore, in the systems of
scalar-quark hadrons and chimera hadrons, scalar-quarks acquire large mass due
to large quantum corrections by gluons. Together with other evidences of mass
generations of glueballs and charmonia, we conjecture that all colored
particles generally acquire a large effective mass due to dressed gluon
effects.Comment: 9 pages, 9 figure
Chiral symmetry restoration and axial vector renormalization for Wilson fermions
Lattice gauge theories with Wilson fermions break chiral symmetry. In the
U(1) axial vector current this manifests itself in the anomaly. On the other
hand it is generally expected that the axial vector flavour mixing current is
non-anomalous. We give a short, but strict proof of this to all orders of
perturbation theory, and show that chiral symmetry restauration implies a
unique multiplicative renormalization constant for the current. This constant
is determined entirely from an irrelevant operator in the Ward identity. The
basic ingredients going into the proof are the lattice Ward identity, charge
conjugation symmetry and the power counting theorem. We compute the
renormalization constant to one loop order. It is largely independent of the
particular lattice realization of the current.Comment: 11 pages, Latex2
Instantaneous Interquark Potential in Generalized Landau Gauge in SU(3) Lattice QCD: A Linkage between the Landau and the Coulomb Gauges
We investigate in detail "instantaneous interquark potentials", interesting
gauge-dependent quantities defined from the spatial correlators of the temporal
link-variable , in generalized Landau gauge using SU(3) quenched lattice
QCD. The instantaneous Q potential has no linear part in the
Landau gauge, and it is expressed by the Coulomb plus linear potential in the
Coulomb gauge, where the slope is 2-3 times larger than the physical string
tension. Using the generalized Landau gauge, we find that the instantaneous
potential can be continuously described between the Landau and the Coulomb
gauges, and its linear part rapidly grows in the neighborhood of the Coulomb
gauge. We also investigate the instantaneous 3Q potential in the generalized
Landau gauge, and obtain similar results to the Q case. -length
terminated Polyakov-line correlators and their corresponding "finite-time
potentials" are also investigated in generalized Landau gauge
Kompetenzorientierung im europĂ€ischen Bildungsraum:RĂŒckschlĂŒsse fĂŒr eine moderne Hochschuldidaktik
Die vorliegende Masterarbeit greift aktuelle bildungspolitische Entwicklungen auf und leistet einen Beitrag zur Strukturierung der historisch gewachsenen Ausgangslage der Hochschuldidaktik in Deutschland. Besondere BerĂŒcksichtigung finden aktuelle bildungspolitische Entwicklungen und damit einhergehende Forderungen auf Ebene der Hochschullehre. Detailliert wird auf die BeschlĂŒsse im Rahmen der Bologna-Reform eingegangen und aus einer erwachsenenpĂ€dagogischen Perspektive folgende Fragestellung diskutiert: Welche RĂŒckschlĂŒsse lassen sich aus den Diskursen im europĂ€ischen Bildungsraum unter BerĂŒcksichtigung des historisch gewachsenen Kontextes von Hochschuldidaktik fĂŒr die Konstruktionsebene einer modernen Hochschuldidaktik ableiten? Es wird analysiert, welche Konsequenzen sich aus den bildungspolitischen Forderungen fĂŒr die Ebene der Gestaltung und Organisation universitĂ€rer Hochschullehre ableiten lassen. Dazu zĂ€hlen besonders didaktischen Forderungen, die sich aus der angestrebten Kompetenz- bzw. Lernergebnisorientierung ergeben. <br
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